Method of manufacturing a radiation-sensitive electronic device

ABSTRACT

A METHOD OF PROVIDING A RADIATION-PERMEABLE CONTACT LAYER IN GOOD ELECTRICAL CONTACT WITH RADIATION-SENSITIVE OR ELECTROLUMINESCENT GRAINS, THE GRAINS BEING SPREAD ON A METAL LAYER WHICH IS SITUATED ON A RADIATION-PERMEABLE CONDUCTIVE LAYER, AND UPON HEATING IN THE MELTED CONDITION THE MELTED METAL OF THE METAL LAYER IS DRAWN BY CAPILLARY ACTION TO BETWEEN THE GRAINS AND THE PERMEABLE CONDUCTIVE LAYER AND THE SPACE BETWEEN THE GRAINS IS THEN FILLED WITH A POLYURETHANE.

April 24, 1973 T, s, TE VELDE 3,729,342

METHOD OF MANUFACTURING A RADIATION-SENSITIVE ELECRONIC DEVICE FiledApril 1, 1970 INVENTOR.

TIES S.TE VELDE E@ Awe@ United States Patent Office 3,729,342 PatentedApr. 24, 1973 3,729,342 METHOD F MANUFACTURING A RADIATION- SENSITIVEELECTRGNIC DEVICE Ties Siebolt te Velde, Emmasingel, Eindhoven,Netherlands, assignor to U.S. Philips Corporation, New York,

Filed Apr. 1, 1970, Ser. No. 24,556 Claims priority, applicationNetherlands, Apr. 16, 1969, 6905835 Int. Cl. B44d 1/16 U.S. Cl. 117-2176 Claims ABSTRACT 0F THE DISCLOSURE The invention relates to a method ofmanufacturing a radiation-sensitive or electroluminescent electronicdevice which comprises a foil consisting of radiation-sensitive orelectroluminescent grains, for example, semiconductor grains which areincorporated in an insulating binder surface portions of said grainsbeing free from the binder on at least one side of the foil, said foilbeing covered at least on said side with a contact layer whichelectrically interconnects said grains, the contact layer beingpermeable to radiation to which the grains are sensitive or which can beemitted by the grains.

The invention furthermore relates to a device manufactured by using themethod according to the invention.

Devices as described above are known, and may be used, for example, inradiation detectors, photoresstors, solar batteries andelectroluminescent panels. Ihe said radiation may be of anelectromagnetic or corpuscular nature.

In manufacturing such a device, on the one hand the grains must be fixedupon forming the foil while on the other hand the radiation-permeablecontact layer must be provided on the foil in such manner that a goodelectric contact with the grains is obtained.

In known methods a rather large number of more or less complicatedoperations are used for that purpose, in which first the grains areembedded in the binder, parts of grains being then liberated from thebinder on at least one side and finally a radiation-permeable contactlayer is provided on said side usually in several operation steps.

One of the objects of the invention is to provide a very simple methodin which the desirable result is obtained with a minimum number ofoperation steps.

The invention is based inter alia on the discovery that by using acomparatively low-melting-point metal layer and making use of capillaryforces, the fixing of the grains and the provision of aradiation-permeable contact layer in good electric contact with thegrains can be carried out in one operation step.

.According to the invention, a method of the type mentioned in thepreamble is therefore characterized in that on a first electricallyconductive layer which is permeable to the said radiation a second layeris provided of a metal which, in the melted condition, Wets the firstlayer less readily than the grains, the grains are spread on the secondlayer, the metal of the second layer is then melted and contractsbetween the grains and the first layer due to the occurring capillaryforces and is substantially removed from the parts of the first layersituated between the grains, that after cooling the non-adhered grainsare removed and that a binder permeable to said radiation is thenprovided in the spaces between the grains. Of course the thickness ofthe metal layer must be chosen to be so that the grainscannot entiresink away in the metal.

Metals for fixing and contacting the grains are those metals and alloyshaving a lower melting-point than the grains and the firstradiation-permeable conductive layer. Particularly useful are metalsthose having a melting point below 1000 C., for example, Zn, Cd, Ga, In,Tl, Sn, Pb, Sb, Bi and Te.

With a given grain material the metals chosen are those which readilywet the grains and therefore can give a good adhesion and a goodelectric contact with the grains. Of course, low melting-point metalswhich have an undesired reaction with the materials with which they arecontacted, cannot be used.

As is known from semiconductor technology, the possibility is availableby the choice of the metals and possible additions to said metals, toform both ohmic and rectifying contacts on the grains in so far as theseare active as semiconductors.

Light-permeable conductive oxide layers can be used for the said firstradiation-permeable conductive layer. For example, layers of tin oxideand/or indium oxide, which can be realized by spraying with a solutionof tin chloride and indium chloride, respectively, or by vapourdeposition in known manner. The electric conductivity is effected byadditions, such as antimony or boron, or as a result of deviations fromthe stoichiometric composition caused during the provision. Furthermore,thin light-permeable metal layers, for example, gold layers, may be usedin many cases.

In general the first radiation-permeable conductive layer will beprovided on a support during the manufacture. If this support is at bestsparingly permeable to the said radiation, it will have t0 be removed atthe end of the operation. According to an important preferredembodiment, however, the first layer is provided on a support which ispermeable to the said radiation and need therefore not be removed fromthe foil.

Of course, the composition of the first transparent layer must be chosento be such as not to dissolve in an undesired manner in the metal to beused. However, the possibility of choice is so wide than in this respectno difficulties need to occur.

The invention will now be described with reference to the accompanyingdrawing, in which FIG. 1 is a diagrammatic cross-sectional view of astage of the method according to the invention, and

FIG. 2 is a diagrammatic cross-sectional view of a device manufacturedby using the method according to the invention.

A layer of indium oxide 2 is vapour-deposited on a glass support asshown in FIG. 1. This is carried out by evaporating indium oxide at C.in an atmosphere which contains oxygen at a pressure of 5.10-4 mm.mercury. The support 1 is kept at a temperature of 300 C. Thus a layer 2is obtained which is light-permeable and electrically conductive.

On this layer a layer of cadmium 3, 500 A. thick, is then provided byvapour deposition in a vacuum at 500 C. Zinc selenide 4 in powder formhaving an average grain size of 30 um. is scattered on said layer.

After heating for 30 minutes at 450 C. in hydrogen of atmosphericpressure, the grains contacting the metal 3 adhere to the support as isshown in FIG. 2, as a result of which a mono-grain layer is formed afterremoving the non-adhering grains.

The cadmium 3 which forms an ohmic contact with the grains is drawn awayfrom the iridium oxide between the grains by the occurring capillaryforces, and interruptions are formed in the metal layer 3. As a resultof this, transmission of radiation from and to the grains 4 can takeplace.

The layer of grains 4 is then impregnated with a mixture of componentswhich form a polyurethane 6. After partial hardening of the polyurethanethe grain surfaces are cleaned by etching with an alcoholic lye solutionand entirely hardened.

Finally a copper layer 7 is vapour-deposited which forms rectifyingcontacts with the grains `4 of zinc selenide.

The resulting assembly may be used, for example, as anelectroluminescent panel.

It will be obvious that the invention is not restricted to the examplesdescribed, but that many variations are possible to those skilled in theart by choosing other combinations of materials without departing fromthe scope of this invention. For example, by a suitable choice of themetal 3 and the grain material 4 in FIG. 2, a photosensitive orradiating rectifying contact instead of an ohmic contact can be obtainedbetween the metal 3 and the grains 4, an ohmic contact being preferablye'iected between the metal 7 and the grains 4. The contact layer 7 maybe omitted, if desirable, for example, if in the operating condition onthis side of the foil charge transport from or to the grains takes placein a diierent manner, for example, by an electron or iron beam, anelectrolyte or analogous charge-transporting means.

What is claimed is:

1. A method of manufacturing a radiation-sensitive electronic devicehaving electrically responsive grains of a radiation-sensitive materialincorporated in an insulating binder comprising the steps of depositingon a support a iirst electrically-conductive radiation permeable layer,

depositing a second layerof a metal, depositing -radiationsensitivegrains on said metal layer, melting the metal layer whereby thoseportions of the metal layer not in contact with at least one of thegrain are drawn by capillary action to substantially accumulate betweenthose grains which are in contact with the metal layer substantiallyremoving the metal between those grains in contact with the metal layerto form separate metal layers for each 0f those grains, cooling themetal layers to solidify the same, removing the remaining grains notcontacting said metal layers, and thereafter impregnating the spacesbetween those grains with an insulating binder.

2. A method as claimed in claim 1 wherein the rst layer is provided on asupport which is permeable to the said radiation.

3. A method as claimed in claim 1 wherein the metal of the second layerhas a melting point lower than 1000 C.

4. A method as claimed in claim 1 wherein the grains areelectroluminescent.

5. A method as claimed in claim 1 wherein the grains are photosensitive.

6. A method as claimed in claim S wherein the radiation permeable layeris indium oxide and the metal iS cadmium.

References Cited UNITED STATES PATENTS 2,881,344 4/1959 Michlin 313-108A 3,108,202 10/ 1963 Farnsworth 313-65 A 3,408,223 10/ 1968 Shortes117-100 B ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH,Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No.3172923142 Dated April 2,4-, 1973 Inventor(s) Ties T6 Velde It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line l1, "useful are metals those" should read --useful arethose metals".

Column 3,V line 2, "iridium oxide" should read --indium oxide-"H Signedland seald this 25th day of June 19714.

(SEAL) Attest:

EUNARD M.FLETCH.`ER,JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents ORM PO-1050 (1D-69) USCOMMDC 60376P69 U.S. GOVERNMENTPRINTING OFFICE 199 O-SGG-SB,

